Impulse generator and method for perforating a cased wellbore

ABSTRACT

An impulse generator ( 76 ) and method for using an impulse generator ( 76 ) to initiate a detonation in a shaped charge perforating apparatus ( 60 ) is disclosed. The shaped charge perforating apparatus ( 60 ) is adapted for use in a wellbore ( 62 ) and includes a plurality of shaped charges ( 86 ). A detonation cord ( 98 ) is operably coupled to each of the shaped charges ( 86 ). An initiator ( 78 ) is operable to detonate the detonation cord ( 98 ) upon receiving a triggering impulse. A Marx generator within the impulse generator ( 76 ) provides the triggering impulse to the initiator ( 78 ).

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates, in general, to perforating a casedwellbore that traverses a subterranean hydrocarbon bearing formationand, in particular, to an impulse generator for generating a dischargevoltage impulse for the initiation of a detonation in order tofacilitate the perforation of a cased subterranean wellbore using shapedcharges.

BACKGROUND OF THE INVENTION

[0002] Without limiting the scope of the present invention, itsbackground will be described with reference to perforating asubterranean formation with a shaped charge perforating apparatus, as anexample.

[0003] After drilling a section of a subterranean wellbore thattraverses a formation, individual lengths of relatively large diametermetal tubulars are typically secured together to form a casing stringthat is positioned within the wellbore. This casing string increases theintegrity of the wellbore and provides a path for producing fluids fromthe producing intervals to the surface. Conventionally, the casingstring is cemented within the wellbore. To produce fluids into thecasing string, hydraulic openings or perforations must be made throughthe casing string, the cement and a short distance into the formation.

[0004] Typically, these perforations are created by detonating a seriesof shaped charges that are disposed within the casing string and arepositioned adjacent to the formation. Specifically, one or more chargecarriers are loaded with shaped charges that are connected with adetonating device, such as a primacord or detonation cord. The chargecarriers are then connected within a tool string that is lowered intothe cased wellbore at the end of a tubing string, wireline, slick line,coil tubing or other conveyance. Once the charge carriers are properlypositioned in the wellbore such that the shaped charges are adjacent tothe formation to be perforated, the shaped charges may be fired.

[0005] The shaped charges used to perforate the casing include highexplosives and must therefore be handled with extreme caution. Forexample, it is imperative that the high explosives are not prematurelyinitiated causing the shaped charge to detonate. Accordingly, in theinterest of safety, initiators that are considerably insensitive toelectric current are typically used to initiate the shaped chargedetonations.

[0006] For example, initiators that are operated using extremely highvoltage and current have been used in order to avoid inadvertentdetonation of shaped charges. Such high voltage and current initiatorsare substantially immune from any naturally occurring energy sources inthe environment which cannot produce the voltage and current necessaryto initiate these devices. Specialized electronic circuitry capable ofproducing the extremely high voltage and current necessary to initiatethese initiators is employed to commence the detonation. Typically, theelectronic circuitry includes integrated circuitry housed in aprotective casing.

[0007] It has been found, however, that due to the power levels requiredto initiate these initiators, the existing electronic circuitry hasseveral drawbacks. In order to produce the necessary electric currentand voltage, the existing semiconductor based electronic circuitry isbulky and expensive. Moreover, a protective casing must be employed toensure the functionality of the circuitry at elevated downholetemperatures and pressures. In addition, to be cost effective, theprotective casing must enable the electronic circuitry to survive thefiring of the shaped charges such that the electronic circuitry and itsprotective casing may be reused.

[0008] In order to survive the detonation of the shaped charges,conventional designs place the electronic circuitry at or near the topof the string away from the initiator. A specialized coaxial cable orflat cable having a low resistance and low inductance connects theelectronic circuitry to the initiator in order that the high voltage andcurrent pulse may be fully conducted. The specialized cabling necessaryto conduct the voltage impulse adds further engineering and expense tothe existing detonation schemes. Accordingly, it has been found that theuseful life of these systems makes their use uneconomical due to thelikelihood of damage caused during the perforation process.

[0009] Therefore a need has arisen for a system and method forgenerating a discharge voltage impulse for the initiation of adetonation that is insensitive to electrical currents and which preventsaccidental triggering of the detonation. Further, a need has arisen forsuch a system and method that is inexpensive enough to be suitable forsingle use operations and that is compact enough to be easily loweredinto a wellbore along with a perforating gun string. Additionally, aneed has arisen for such a system and method that is capable ofwithstanding the great temperatures and pressures in a downholeenvironment prior to its operation.

SUMMARY OF THE INVENTION

[0010] The present invention disclosed herein comprises a shaped chargeperforating apparatus and a method for perforating a cased wellbore thatare capable of generating a discharge voltage impulse for the initiationof a detonation using an initiator that is insensitive to electricalcurrents. The apparatus of the present invention is compact enough to beeasily lowered into a wellbore, is able to withstand downholetemperatures and pressures and, due to its inexpensive construction, theapparatus is expendable.

[0011] The shaped charge perforating apparatus of the present inventionachieves these results by employing a Marx generator to create a voltageimpulse which is applied to the initiator. The shaped charge perforatingapparatus comprises multiple shaped charges and a detonation cordoperably coupled to each of the shaped charges. The initiator isoperable to initiate a detonation within the detonation cord uponreceiving a triggering impulse such as the discharge voltage impulsefrom the Marx generator.

[0012] The Marx generator comprises an input terminal, an outputterminal coupled to the initiator and a series of capacitors connectedin series between the input terminal and the output terminal. Multiplesurge arrester components are connected between the capacitors inseries, and another arrester component is positioned between the lastone of the capacitors and the output terminal. The capacitors areoperable to be charged in parallel via the charging resistors anddischarged in series.

[0013] The Marx generator has multiple stages whereby the dischargevoltage impulse is proportional to the number of stages times a chargingvoltage that is applied to the Marx generator. Upon receiving asufficient charging voltage, the Marx generator is operable to enterregenerative latch up. In one embodiment, each stage comprises onecapacitor and one surge arrester component. In another embodiment, thesurge arrester components may include gas surge arrester tubes.Additionally, the capacitors may include a ceramic material having adielectric coefficient that increases with temperature.

[0014] In a further embodiment, the present invention is directed to amethod for delivering a discharge voltage impulse to an initiator thatinitiates a detonation in a detonation cord connected to a series ofshaped charges positioned in a wellbore. The method includes the stepsof positioning an impulse generator in a wellbore, applying a chargingvoltage to the input terminal, charging the plurality of capacitors inparallel through the charging resistors and discharging the capacitorsin series by the simultaneous spark over of the surge arrestercomponents, thereby delivering a discharge voltage impulse to theinitiator via the output terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more complete understanding of the features and advantagesof the present invention, reference is now made to the detaileddescription of the invention along with the accompanying figures inwhich corresponding numerals in the different figures refer tocorresponding parts and in which:

[0016]FIG. 1 is schematic illustration of an offshore oil and gasplatform operating a shaped charge perforating apparatus of the presentinvention;

[0017]FIG. 2 is a side view partially cut away of a shaped chargeperforating apparatus adapted for use in a wellbore of the presentinvention;

[0018]FIG. 3 is a cross sectional view of an exploding foil typeinitiator as used in the shaped charge perforating apparatus of thepresent invention;

[0019]FIG. 4A is a top plan view of an exploding foil or slapperinitiator for use in the shaped charge perforating apparatus of thepresent invention;

[0020]FIG. 4B is a top plan view of a second exploding foil or slapperinitiator for use in the shaped charge perforating apparatus of thepresent invention;

[0021]FIG. 4C is a top plan view of a third exploding foil or slapperinitiator for use in the shaped charge perforating apparatus of thepresent invention;

[0022]FIG. 4D is a top plan view of a fourth exploding foil or slapperinitiator for use in the shaped charge perforating apparatus of thepresent invention;

[0023]FIG. 5 is a cross sectional view of a bridgewire type initiator asused in the shaped charge perforating apparatus of the presentinvention;

[0024]FIG. 6 is a side view partially in cross section of a Marxgenerator for generating a discharge voltage impulse in accordance withthe teachings of the present invention; and

[0025]FIG. 7 is a circuit diagram of an impulse generator circuitelectrically coupled to an initiator for generating a discharge voltageimpulse and initiating a detonation in accordance with the teachings ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts whichcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention, and do not delimit the scope of the presentinvention.

[0027] Referring initially to FIG. 1, a shaped charge perforatingapparatus adapted for use in a wellbore operating from an offshore oiland gas platform is schematically illustrated and generally designated10. A semi-submersible platform 12 is centered over a submerged oil andgas formation 14 located below sea floor 16. A subsea conduit 18 extendsfrom deck 20 of platform 12 to wellhead installation 22 includingblowout preventers 24. Platform 12 has a hoisting apparatus 26 and aderrick 28 for raising and lowering pipe strings.

[0028] A wellbore 36 extends through the various earth strata includingformation 14. Casing 38 is cemented within wellbore 36 by cement 40.When it is desired to perforate casing 38 adjacent to formation 14, ashaped charge perforating apparatus 42 is lowered into casing 38 viaelectrical line 44. Thereafter, an electric signal is sent to an impulsegenerator 46 which, in turn, sends a discharge voltage impulse toinitiator 48. Initiator 48 initiates the detonation of the shapedcharges that are disposed within shaped charge perforating apparatus 42.Upon detonation, perforations are created that extend outwardly throughcasing 38, cement 40 and into formation 14.

[0029] Even though FIG. 1 depicts a vertical well, it should be noted byone skilled in the art that the shaped charge perforating apparatus ofthe present invention is equally well-suited for use in wells havingother geometries such as deviated wells, inclined wells or horizontalwells. Also, even though FIG. 1 depicts an offshore operation, it shouldbe noted by one skilled in the art that the shaped charge perforatingapparatus of the present invention is equally well-suited for use inonshore operations.

[0030] Referring now to FIG. 2, therein a shaped charge perforatingapparatus 60 is illustrated positioned in a wellbore 62 that penetratesformation 64. A casing 66 lines wellbore 62 and is secured in positionby cement 68. A fluid such as drilling fluid (not shown) fills theannular region between shaped charge perforating apparatus 60 and casing66. An electric line 70 is coupled to shaped charge perforatingapparatus 60 at a cable head 72. A collar locator 74 is positioned belowcable head 72 to aid in the positioning of shaped charge perforatingapparatus 60 in wellbore 62. An impulse generator 76 is coupled tocollar locator 74 and is in electrical communication with the surfacevia electric line 70.

[0031] An initiator 78 is mechanically and electrically coupled toimpulse generator 76. Upon receiving a triggering impulse, initiator 78is operable to initiate the detonation of shaped charge perforatingapparatus 60. Initiator 78 may be a bridgewire initiator (BWI), anexploding bridgewire initiator (EBWI), an exploding foil initiator(EFI), a percussion type initiator, a pressure actuated initiator or thelike.

[0032] Shaped charge perforating apparatus 60 includes a perforating gun80 having a carrier 82 made of a cylindrical sleeve having a pluralityof recesses, such as recess 84, defined therein. Radially aligned witheach recess 84 is a respective one of a plurality of shaped charges,such as shaped charge 86. Each of the shaped charges includes an outerhousing, such as housing 88 of shaped charge 86, and a liner, such asliner 90 of shaped charge 86. Disposed between each housing and liner isa quantity of high explosive.

[0033] The shaped charges are retained within carrier 82 by a supportmember 92 which includes an outer charge holder sleeve 94, an innercharge holder sleeve 96. In this configuration, outer charge holdersleeve 94 supports the discharge ends of the shaped charges, while innercharge holder sleeve 96 supports the initiation ends of the shapedcharges. Disposed within inner tube 96 is a detonation cord 98, such asa primacord, which is used to detonate the shaped charges. In theillustrated embodiment, the initiation ends of the shaped charges extendacross the cental longitudinal axis of perforating gun 80 allowingdetonation cord 98 to connect to the high explosive within the shapedcharges through an aperture defined at the apex of the housings of theshaped charges.

[0034] Each of the shaped charges is longitudinally and radially alignedwith a recess 84 in carrier 82 when perforating apparatus 60 is fullyassembled. In the illustrated embodiment, the shaped charges arearranged in a spiral pattern such that each shaped charge is disposed onits own level or height and is to be individually detonated so that onlyone shaped charge is fired at a time. It should be noted, however, bythose skilled in the art that alternate arrangements of shaped chargesmay be used, including cluster type designs wherein more than one shapedcharge is at the same level and is detonated at the same time, withoutdeparting from the principles of the present invention.

[0035] In an operational embodiment, to detonate the shaped charges, anelectrical signal, i.e. a charging voltage, is sent from the surface toimpulse generator 76 via electric line 70. Alternatively, a downholebattery or other power source operably associated with impulse generator76 may provide the electric signal to the impulse generator 76. Afterreceiving the charging voltage, impulse generator 76 executes a voltagemultiplication increasing the voltage and current of the chargingvoltage to generate a discharge voltage impulse. The discharge voltageimpulse is transmitted to initiator 78 which, in turn, initiates adetonation within detonation cord 98 such that the shaped charges arefired.

[0036]FIG. 3 presents an EFI 102 that includes an upper cap portion 104having molded therein two electric conductors 106 and a slapper orinitiator foil 108. Upper cap portion 104 may be formed of a moldedplastic or the like. A flyer 110 is placed over initiator foil 108. Inone embodiment, flyer 110 comprises a thin disk constructed from aninsulating material such as a plastic.

[0037] A barrel 112 is placed over flyer 110 to sandwich flyer 110tightly against initiator foil 108. A housing 114 contains a pressedpellet 116 of a secondary explosive material which is in intimatecontact with barrel 112. It should be noted that the secondary explosivematerial can be handled more safely than conventional primary explosivematerial because it is less sensitive to shock and, accordingly, otherexternal stimuli are less capable of causing premature detonation. Anair gap 120 is positioned within pressed pellet 116. A seal boot 122forms crimps 124 that connect a detonation cord 126 to EFI 102. Sealboot 122 has an internal, hollow, axial passage and external crimps 124formed by crimping the shell around a detonation cord 126. Detonationcord 126 is connected to a set of shaped charges deployed in the shapedcharge perforating apparatus as best seen in FIG. 2.

[0038] Typically, a high voltage, high intensity current electricalimpulse is supplied to electrical conductors 106 by the impulsegenerator in a manner to sufficiently vaporize or cause initiator foil108 to be exploded or vaporized. In response to the pressure generatedby the vaporization gases, flyer 110 penetrates barrel 112 in thefashion of a projectile. Flyer 110 propels down housing 114 until itsufficiently impacts secondary explosive 118, detonating secondaryexplosive 118 which, in turn, detonates detonation cord 126 connected tothe string of shaped charges. It should be understood by those skilledin the art that the EFI may have design modifications. For example, theEFI may have one electric conductor instead of two.

[0039]FIG. 4A illustrates an exemplary configuration of an initiatorfoil 130 of the type that may be employed in the EFI illustrated in FIG.3. A narrow neck 132 is positioned in initiator foil 130 which comprisesa thin sheet of conductive material such as aluminum or copper, forexample. Once the critical breakdown voltage is reached, current flowsacross narrow neck 132 which causes initiator foil 130 to explode orvaporize. FIG. 4B illustrates a second exemplary configuration of aninitiator foil 134 of the type that may be employed in the EFIillustrated in FIG. 3. A narrow neck 136 and a control gap 138 areemployed to facilitate the explosion or vaporization of initiator foil134. Similarly, FIG. 4C illustrates a third exemplary configuration ofan initiator foil 140. A control gap 142 facilitates the vaporization ofinitiator foil 140. FIG. 4D illustrates a fourth exemplary configurationof an initiator foil 144 having narrow necks 146, 148 to facilitatevaporization.

[0040]FIG. 5 presents an BWI 150 that includes a housing 152 havingpositioned therein an electric conductor 154 and a bridgewire ignitor156 that extends from electric conductor 154 into a pressed pellet 158of a primary explosive material. A pressed pellet 162 of a secondaryexplosive material is positioned against pressed pellet 158 of primaryexplosive material. A seal boot 166 forms crimps 168 that connect adetonation cord 170 to BWI 150. Seal boot 166 has an internal, hollow,axial passage and external crimps 168 formed by crimping the shellaround detonation cord 170.

[0041] In an operational embodiment, a charging voltage is supplied toelectrical conductor 154 by the impulse generator in a manner tosufficiently cause bridgewire ignitor 156 to ignite. In response to theheat produced by ignited bridgewire ignitor 156, primary explosivematerial 158 is detonated, which, in turn, detonates secondary explosivematerial 162 and initiates the detonation in detonation cord 170, whichruns into the shaped charge perforating apparatus to fire the shapedcharges.

[0042]FIG. 6 illustrates a Marx generator 180 for generating atriggering impulse in accordance with the teachings of the presentinvention. Capacitors 182-200 are connected in series between an inputterminal 202 and an output terminal 204. Input terminal 202 includes apiece of coaxial cable or other connector and receives the chargingvoltage from an electric line or other downhole power source. Outputterminal 204 includes a piece of coaxial cable or short air gap andtransmits a discharge voltage impulse to the initiator.

[0043] Preferably, capacitors 182-200 comprise a ceramic material havinga dielectric coefficient that increases with temperature. It should beunderstood by those skilled in the art, however, that any device whichconsists essentially of two conductors, such as parallel metal plates,insulated from each other by a dielectric and which introducecapacitance into a circuit, stores electrical energy, blocks the flow ofdirect current and permits the flow of alternating current to a degreedependent on the capacitors' capacitance and the current frequency iswithin the teachings of the present invention.

[0044] Multiple surge arrester components 206-222 are connected betweeneach of capacitors 182-200 in series and an additional surge arrestercomponent 224 is positioned between capacitor 200 and output terminal204. Preferably, surge arrester components 206-224 comprise gas surgearrester tubes. Typically, gas surge arrester tubes have a switchingtime below 50 nanoseconds and exceptionally high peak currents thatproduce steep voltage or current pulses of a few microseconds duration.Moreover, gas surge arrester tubes are inexpensive and capable of onlyone-time use. Accordingly, the disposable qualities of the surgearrester tubes are well suited for downhole use in close proximity toexplosives. Alternatively, surge arrester components 206-224 maycomprise fast-recovery hydrogen spark gaps or any gas-filled switchingspark gap device that is characterized by a very steep current riseduring the breakdown of the switch. The exact values of the capacitorsand resistors will depend on the desired voltage and current of thedischarge voltage impulse.

[0045] A tubular housing 226 cabins capacitors 182-200 and surgearrester tubes 206-224. In one embodiment, tubular housing 226 providesa circuit ground. Additionally, tubular housing 226 protects capacitors182-200 and surge arrester components 206-224 from downhole temperaturesand pressures. In this regard, the construction of Marx generator 180 isideal for downhole use. Marx generator 180 includes no temperaturesensitive components such as the semiconductor components of existingdownhole impulse generators. Accordingly, the lack of temperaturesensitive components translates into an inexpensive housing having asmall profile that can be easily positioned downhole.

[0046] In operation, the charging voltage is applied to Marx generator180 and capacitors 182-200 are charged through charging resisters asshown and explained below with reference to FIG. 7. When capacitors182-200 are fully charged, surge arrester component 206 is broken downfrom overvoltage. This effectively places capacitors 182 and 184 inseries which overvolts the next surge arrester component 208, whichplaces capacitors 182, 184 and 186 in series. This erecting continuesuntil the discharge voltage impulse is transmitted to the initiator.

[0047] Referring now to FIG. 7, an impulse generator circuit 240 forgenerating a discharge voltage impulse is electrically coupled to aninitiator 242. Circuit 240 includes a series of capacitors 244-262positioned in parallel with charging or isolation impedances illustratedas resistors 264-302. Resistors 264-302 may be carbon-compositionresistors for example. It should be understood by those skilled in theart, however, that resistors 264-302 may comprise any device or materialthat offers an opposition to the flow of current, equal to the voltagedrop across the element divided by the current through the element.

[0048] A series of switching elements illustrated as gas surge arrestertubes 304-320 are positioned in series with capacitors 244-262. The lastgas surge arrester tube 322 acts as a peaking switch to isolate circuit240 from the load, i.e. initiator 242, until capacitors 244-262 arecompletely charged and circuit 240 enters regenerative latch up.Additionally, a ground 324 is provided. It should be understood by thoseskilled in the art that the circuit may be constructed of various typesof components and, in particular, the construction may includecomponents not enumerated herein. Similarly, other criteria within thecircuit may be varied.

[0049] In an operational embodiment, a charging voltage is applied toinput terminal 326. Capacitors 244-262 are charged in parallel throughcharging resistors 264-302. The bank of capacitors 244-262 is charged upto the voltage that is applied to input terminal 362. Once capacitors244-262 become charged, circuit 240 enters regenerative latch up atwhich time, capacitors 244-262 are discharged in series by thesimultaneous spark over of gas surge arrester tubes 304-322. The firstgas surge arrester tube 304 is triggered to arc at the desired timewhich causes a regenerative firing of all of the remaining gas surgearrester tubes 306-322 in a very short duration producing an impulsewhich has an extremely fast rise time. This effectively places all ofcapacitors 244-262 in series across the output load, i.e. initiator 242.The duration of the resulting discharge voltage impulse is dependentupon the load resistance and the value of the stage capacitance. In theillustrated embodiment, the stacked array of capacitors 244-262 andsurge arrester tubes 304-322 form a series of ten stages wherein eachstage comprises a capacitor and a surge arrester tube such as capacitor244 and surge arrester tube 304. Circuit 240 performs a voltagemultiplication on the charging voltage to generate the discharge voltageimpulse. The discharge voltage impulse is proportional to the number ofstages times the charging voltage applied to circuit 240. The number ofstages, however, may vary as a design choice that depends upon therequired voltage amplification. A discharge voltage impulse is therebydischarged to initiator 242.

[0050] While this invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is, therefore, intended that the appended claimsencompass any such modifications or embodiments.

What is claimed is:
 1. A shaped charge perforating apparatus adapted foruse in a wellbore, comprising: a plurality of shaped charges; adetonation cord operably coupled to the shaped charges; an initiatoroperable to initiate a detonation within the detonation cord uponreceiving a triggering impulse; and a Marx generator operably associatedwith the initiator that is operable to generate the triggering impulse.2. The shaped charge perforating apparatus as recited in claim 1 whereinthe Marx generator further comprises an input terminal, an outputterminal coupled to the initiator, a plurality of capacitors connectedin series between the input terminal and the output terminal, aplurality of first surge arrester components connected between each ofthe capacitors in series, and a second surge arrester componentpositioned between the last one of the capacitors and the outputterminal.
 3. The shaped charge perforating apparatus as recited in claim2 wherein the plurality of first surge arrester components and thesecond surge arrester component comprise gas surge arrester tubes. 4.The shaped charge perforating apparatus as recited in claim 2 whereinthe plurality of capacitors comprise a ceramic material having adielectric coefficient that increases with temperature.
 5. The shapedcharge perforating apparatus as recited in claim 2 wherein thetriggering impulse is a discharge voltage impulse.
 6. The shaped chargeperforating apparatus as recited in claim 5 wherein the plurality ofcapacitors, the plurality of first surge arrester components and thesecond surge arrester component of the Marx generator comprises aplurality of stages whereby the discharge voltage impulse isproportional to the number of stages times a charging voltage applied tothe Marx generator.
 7. The shaped charge perforating apparatus asrecited in claim 6 wherein each stage comprises one of the capacitorsand one of the first or second surge arrester components.
 8. The shapedcharge perforating apparatus as recited in claim 6 wherein the Marxgenerator is operable to enter regenerative latch up upon receiving thecharging voltage.
 9. The shaped charge perforating apparatus as recitedin claim 1 wherein the initiator is selected from the group consistingof bridge wire initiators, exploding bridge wire initiators, explodingfoil initiators, percussion type initiators and pressure actuatedinitiators.
 10. The shaped charge perforating apparatus as recited inclaim 1 wherein the Marx generator is housed in a tubular housing thatprovides a circuit ground.
 11. An impulse generator for delivering adischarge voltage impulse to an initiator that initiates a detonationwithin a detonation cord connected to a plurality of shaped chargespositionable in a wellbore, the impulse generator comprising: an inputterminal that is operable to receive a charging voltage; an outputterminal coupled to the initiator, the output terminal operable todeliver the discharge voltage impulse; a plurality of capacitorsconnected in series between the input terminal and the output terminal;a plurality of charging resistors connected in parallel with thecapacitors; a plurality of first surge arrester components connectedbetween each of the capacitors in series; and a second surge arrestercomponent positioned between the last one of the capacitors and theoutput terminal, whereby the plurality of capacitors are operable to becharged in parallel through the charging resistors and discharged inseries.
 12. The impulse generator for delivering a discharge voltage asrecited in claim 11 wherein the plurality of first surge arrestercomponents and the second surge arrester component comprise gas surgearrester tubes.
 13. The impulse generator for delivering a dischargevoltage as recited in claim 11 wherein the plurality of capacitorscomprise a ceramic material having a dielectric coefficient thatincreases with temperature.
 14. The impulse generator for delivering adischarge voltage as recited in claim 11 wherein the charging voltage issupplied from a surface location via an electric line.
 15. The impulsegenerator for delivering a discharge voltage as recited in claim 11wherein the plurality of capacitors, the plurality of first surgearrester components and the second surge arrester component define aplurality of stages such that the discharge voltage impulse isproportional to the number of stages times the charging voltage appliedto the input terminal.
 16. The impulse generator for delivering adischarge voltage as recited in claim 15 wherein each stage comprisesone of the capacitors and one of the first or second surge arrestercomponents.
 17. The impulse generator for delivering a discharge voltageas recited in claim 11 wherein the initiator is selected from the groupconsisting of bridgewire initiators, exploding bridgewire initiators,exploding foil initiators, percussion type initiators and pressureactuated initiators.
 18. The impulse generator for delivering adischarge voltage as recited in claim 11 further comprising a housingthat provides protection to the plurality of capacitors, the pluralityof first surge arrester components and the second surge arrestercomponent and provides a circuit ground.
 19. An impulse generator forgenerating a discharge voltage impulse, comprising: an input terminalthat is operable to receive a charging voltage; an output terminaloperable to deliver the discharge voltage impulse; a plurality ofcapacitors connected in series between the input terminal and the outputterminal; a plurality of charging resistors connected in parallel withthe capacitors; a plurality of first surge arrester components connectedbetween each of the capacitors in series; and a second surge arrestercomponent positioned between the last one of the capacitors and theoutput terminal, whereby the plurality of capacitors are operable to becharged in parallel through the charging resistors and discharged inseries.
 20. The impulse generator for generating a discharge voltageimpulse as recited in claim 19 wherein the plurality of first surgearrester components and the second surge arrester component comprise gassurge arrester tubes.
 21. The impulse generator for generating adischarge voltage impulse as recited in claim 19 wherein the pluralityof capacitors comprise a ceramic material having a dielectriccoefficient that increases with temperature.
 22. The impulse generatorfor generating a discharge voltage impulse as recited in claim 19wherein the plurality of capacitors, the plurality of first surgearrester components and the second surge arrester component define aplurality of stages such that the discharge voltage impulse isproportional to the number of stages times the charging voltage appliedto the input terminal.
 23. The impulse generator for generating adischarge voltage impulse as recited in claim 22 wherein each stagecomprises one of the capacitors and one of the first or second surgearrester components.
 24. The impulse generator for generating adischarge voltage impulse as recited in claim 19 further comprising atubular housing that provides a circuit ground.
 25. A method forperforating a well casing that lines a subterranean well, the methodcomprising the steps of: running downhole a shaped charge perforatingapparatus including a plurality of shaped charges, a detonation cordoperably coupled to the shaped charge, an initiator operable to detonatethe detonation cord and a Marx generator operably associated with theinitiator; supplying a charging voltage to the Marx generator togenerate a discharge voltage impulse; transmitting the discharge voltageimpulse to the initiator; initiating a detonation within the detonationcord; and detonating the shaped charges, thereby perforating the wellcasing that lines the subterranean well.
 26. The method as recited inclaim 25 wherein the step of supplying a charging voltage to the Marxgenerator to generate a discharge voltage impulse further comprises thestep of triggering the Marx generator to enter regenerative latch up.27. The method as recited in claim 25 wherein the step of supplying acharging voltage to the Marx generator to generate a discharge voltageimpulse further comprises the step of executing a voltage multiplicationon the charging voltage to generate the discharge voltage impulse. 28.The method as recited in claim 25 wherein the step of supplying acharging voltage to the Marx generator to generate a discharge voltageimpulse further comprises supplying the charging voltage to an inputterminal, charging a plurality of capacitors connected in series betweenthe input terminal and an output terminal, overvolting a plurality offirst surge arrester components connected between each of the capacitorsin series and a second surge arrester component positioned between thelast one of the capacitors and the output terminal and generating thedischarge voltage impulse at the output terminal.
 29. The method asrecited in claim 28 wherein the plurality of first surge arrestercomponents and the second surge arrester component comprise gas surgearrester tubes.
 30. The method as recited in claim 28 wherein theplurality of capacitors comprise a ceramic material having a dielectriccoefficient that increases with temperature.
 31. The method as recitedin claim 28 wherein the step of charging the plurality of capacitorsconnected in series between the input terminal and the output terminalfurther comprises the step of charging the plurality of capacitors inparallel via charging resistors.
 32. The method as recited in claim 28wherein the step of generating the discharge voltage impulse at theoutput terminal further comprises the step of discharging the pluralityof capacitors in series.
 33. The method as recited in claim 32 whereinthe step of discharging the plurality of capacitors in series furthercomprises discharging the capacitors in series by the simultaneous sparkover of the first and the second surge arrester components.
 34. Themethod as recited in claim 25 further comprising the step of selectingthe initiator from the group consisting of bridgewire initiators,exploding bridgewire initiators, exploding foil initiators, percussiontype initiators and pressure actuated initiators.
 35. A method fordelivering a discharge voltage impulse to an initiator that detonates adetonation cord connected to a plurality of shaped charges positioned ina wellbore, the method comprising the steps of: positioning an impulsegenerator in a wellbore, the impulse generator including an inputterminal, an output terminal coupled to the initiator, a plurality ofcapacitors connected in series between the input terminal and the outputterminal, a plurality of first surge arrester components connectedbetween each of the capacitors in series and a second surge arrestercomponent positioned between the last one of the capacitors and theoutput terminal; applying a charging voltage to the input terminal;charging the plurality of capacitors in parallel through chargingresistors; and discharging the capacitors in series by the simultaneousspark over of the first and second surge arrester components, therebydelivering the discharge voltage impulse to the initiator via the outputterminal.
 36. The method as recited in claim 35 further comprising thestep of triggering the impulse generator to enter regenerative latch up.37. The method as recited in claim 35 further comprising the step ofexecuting a voltage multiplication on the charging voltage to generatethe discharge voltage impulse.
 38. The method as recited in claim 35wherein the plurality of first surge arrester components and the secondsurge arrester component comprise gas surge arrester tubes.
 39. Themethod as recited in claim 35 wherein the plurality of capacitorscomprise a ceramic material having a dielectric coefficient thatincreases with temperature.
 40. The method as recited in claim 35wherein the impulse generator further comprises a housing that providesa circuit ground.